In recent years, TPMSs (Tire Pressure Monitoring Systems) that detect the air pressures of a plurality of tires provided on a vehicle and emit a warning or the like to a user in the case where the detected air pressure is abnormal have been available. For example, a TPMS includes a transmission apparatus that detects the air pressure of a tire and wirelessly transmits the detected air pressure, and an in-vehicle reporting apparatus that receives the air pressure wirelessly transmitted from the transmission apparatus and performs reporting that depends on the received air pressure. Generally, the transmission apparatus is disposed on a tire wheel provided on the vehicle and detects the air pressure of a tire mounted on the tire wheel. The in-vehicle reporting apparatus, for example, reports the received air pressure to the user as the air pressure of the tire from which the air pressure was detected.
A TPMS (tire pressure monitoring apparatus) described in JP 2006-159961A includes means for registering a tire identification code that identifies each of a plurality of tires that are provided on a vehicle in a memory, and means for judging that a tire has been replaced. This TPMS updates the tire identification code registered in the memory in the case where it is judged that a tire has been replaced. Accordingly, the TPMS described in JP 2006-159961A is able to prevent errors in the correspondence relationship of received air pressures and tires, even in the case where the position of a tire with respect to the vehicle changes as a result of tire rotation or the like, for example, by updating the tire identification code. Thus, the TPMS described in JP 2006-159961A is able to report the air pressure without mistaking the tire from which the air pressure was detected.
However, with the TPMS described in JP 2006-159961A, a special configuration such as a contact switch or an infrared switch provided on the axle needs to be used, in order for the means for judging that a tire has been replaced to judge whether the tire wheel is attached to the vehicle. Thus, with the TPMS of JP 2006-159961A, there is a problem in that costs concerning the configuration of the system increase, due to needing to provide the special configuration. Also, the air pressure monitoring apparatus needs to receive a signal that is transmitted depending on the operating state of a centrifugal force sensor provided in the transmission apparatus (tire pressure sensor). Thus, with the TPMS of JP 2006-159961A, in the case where the air pressure monitoring apparatus is not able to receive this signal, the judging means is not able to judge that the tire has been replaced, and there is a risk of performing erroneous reporting, due to the correspondence relationship of the received air pressure and the tire from which the air pressure was detected being in error.
An object of the instant invention is to provide an in-vehicle reporting apparatus and a reporting system that are able to prevent errors in reporting that depends on acquired air pressure information, when air pressure information related to respective air pressures of a plurality of tires provided on a vehicle is acquired, and to suppress an increase in costs concerning the configuration.